In the development of radio communication systems, in particular cellular communication (like for example GSM (Global System for Mobile Communication), GPRS (General Packet Radio Service), HSPA (High Speed Packet Access), UMTS (Universal Mobile Telecommunication System) or the like), efforts are made for an evolution of the radio access part thereof. In this regard, the evolution of radio access networks (like for example the GSM EDGE radio access network (GERAN) and the Universal Terrestrial Radio Access Network (UTRAN) or the like) is currently addressed. Such improved radio access networks are sometimes denoted as evolved or advanced radio access networks (like for example the Evolved Universal Terrestrial Radio Access Network (E-UTRAN)) or as being part of a long-term evolution (LTE) or LTE-Advanced, also generally referred to as International Mobile Communications—Advanced (IMT-A). Although such denominations primarily stem from 3GPP (Third Generation Partnership Project) terminology, the usage thereof hereinafter does not limit the respective description to 3GPP technology, but generally refers to any kind of radio access evolution irrespective of the underlying system architecture.
In the following, for the sake of intelligibility, LTE (Long-Term Evolution according to 3GPP terminology) or, specifically, LTE-Advanced is taken as a non-limiting example for a radio access network of cellular type being applicable in the context of the present invention and its embodiments. However, it is to be noted that any kind of radio access network of cellular type, such as GSM, GPRS, HSPA and/or UMTS, may likewise be applicable, as long as it exhibits comparable features and characteristics as described hereinafter.
In the development of cellular systems in general, and access networks in particular, heterogeneous network environments, also referred to as multi-layer cellular network systems, comprising a combination of macrocells and microcells (also referred to as relaycells, picocells or femtocells) are proposed as one concept. Thereby, the macrocells (having high transmit power) typically provide for a large geographical coverage, while the microcells (having low transmit power) typically provide for additional capacity of low geographical coverage in areas with a high user deployment. In the context of LTE or LTE-Advanced, the macrocells are typically deployed by base stations denoted as eNBs, while microcells are typically deployed by home base stations denoted as HeNBs. Such heterogeneous network environment may, thus, be considered to be composed at least of two network layers, i.e. a microcell layer and an overlay macrocell layer.
The two network layers of a heterogeneous network environment, i.e. the base stations and/or cells of the two network layers, may be implemented by the same or different radio access technologies. For example, a heterogeneous network environment may be composed of a GSM-based macrocell layer and a LTE-based microcell layer.
FIG. 1 shows a schematic diagram of a deployment scenario of a heterogeneous network environment comprising a combination of macrocells and microcells. In FIG. 1, macrocells are illustrated by hexagonal blocks, while microcells are illustrated by rectangular blocks. In the dashed circle, an enlarged view of a microcell including a microcell base station and a user equipment is illustrated.
In the development of cellular systems in general, and access networks in particular, e.g. in the framework of heterogeneous network environments, carrier aggregation is proposed as one concept. Thereby, both a primary carrier and one or more secondary (non-primary) carriers are used simultaneously by a terminal, wherein the control is derived from the primary carrier.
In this regard, a primary carrier is a standalone carrier which is configured to convey all control information required to operate the system (typically to allow network entry and preliminary exchange to establish a session). Typical information needed to be transmitted over the primary carrier includes broadcast channel, random access channel, map information, etc. A secondary (non-primary) carrier is an additional carrier that could be assigned by the system (i.e. the base station) to a terminal to increase its data rate. Therefore, primary carriers must be fully configured, and a secondary (non-primary) carrier could be either fully configured or partially configured, depending on the deployment scenario. For instance, a fully configured carrier could act as a primary carrier for a specific terminal while being used as a secondary (non-primary) carrier for another terminal.
In the following, carrier aggregation is assumed as the mode of carrier deployment of radio access networks of cellular type being applicable in the context of the present invention and its embodiments.
In certain cases, secondary (non-primary) carriers might for example be deployed in areas with high and unpredictable interference. In such cases, the reliability of control channels and/or signals (of secondary carriers) could be endangered and lead to poor system performance.
The problem of high and unpredictable interference has already received a lot of attention in standardization. In the context of carrier aggregation, it has been agreed to support cross carrier scheduling which allows that certain control channels can be transmitted on one carrier while allocating data transmission on another carrier. The feature of cross carrier scheduling is capable of solving problems regarding the control channel reliability for control channels such as PDCCH (Physical Downlink Control Channel), PCFICH (Physical Control Format Indicator Channel), PHICH (Physical Hybrid-ARQ Indicator Channel; ARG: Automatic Repeat Request), and PUCCH (Physical Uplink Control Channel).
However, a problem with the feature of cross carrier scheduling is that common physical control channels and/or signals, such as PBCH (Physical Broadcast Channel), SSS (Secondary Synchronization Signal) and PSS (Primary Synchronization Signal), may not benefit and, thus, are still subject to the high and unpredictable interference.
In this regard, the key issue is that the transmission of the aforementioned common physical control channels and/or signals may not rely on conventional ICIC (Inter-Cell Interference Coordination) methods, but they need to be transmitted on specific, well-defined, resources. Further, the aforementioned common physical control channels and/or signals may not be muted or in other ways orthogonally allocated between neighboring cells.
The aforementioned common physical control channels and/or signals may be used by terminals for the purposes of synchronization, cell search/detection, radio resource management (RRM) related measurements and/or data channel demodulation. Accordingly, the fact that the interference situation for the aforementioned common physical control channels and/or signals may not be improved by conventional interference avoidance techniques may lead to problems in synchronization, cell search/detection, radio resource management (RRM) related measurements and/or data channel demodulation, particularly at the terminal side.
If the transmission of the aforementioned common physical control channels and/or signals is heavily interfered, then the terminals relying on these channels and/or signals may not be able to access the respective carrier (e.g. the respective secondary carrier). In this regard, it is to be noted that terminals may for example try to validate synchronization by a successful decoding of the PBCH.
In the same stage/context, a terminal may also try to obtain a cell (physical) ID from a decoding of the SSS, and may also try to obtain MIB (Master Information Block) information from the PBCH, including downlink system bandwidth, PHICH configuration, system frame number, etc. With successful decoding of the PBCH, a terminal may also obtain antenna ports configuration of a base station (such as a eNB) which is masked with CRC (Cyclic Redundancy Check) according to the number of transmit antennas ports at the base station (such as the eNB).
All of the above-mentioned operations, i.e. operations in the context of synchronization, cell search/detection, radio resource management (RRM) related measurements and/or data channel demodulation, suffer from interference of the aforementioned common physical control channels and/or signals (especially, but not exclusively, in the framework of carrier aggregation when selecting a non-primary carrier, i.e. when trying to camp on a non-primary cell).
In this regard, it could be conceivable that, as has been already discussed in standardization, the system information of a secondary (non-primary) carrier may be transmitted via RRC (Radio Resource Control) configuration signaling when adding the secondary (non-primary) cell/carrier to the primary cell/carrier in carrier aggregation. However, such an approach has the drawback that it is based on a RRC (Radio Resource Control) signaling rather than a PHY/MAC (Physical layer/Medium Access Control) signaling. Further, such an approach has the drawback that it is not applicable for certain ones of the aforementioned common physical control channels and/or signals (such as e.g. the PSS and the SSS), and thus the terminal synchronization with a secondary (non-primary) carrier is not able to be applied. Still further, such an approach has the drawback that it does not relate to the transmission/provision of the cell (physical) ID information as well as the antenna ports configuration of the base station to the terminal. Accordingly, such an approach is not capable of solving the entirety of the above-mentioned problems and, thus, may not provide for a comprehensive and/or overall solution in view of the above-outlined situation.
In view of the above, there are several problems in terms of high and unpredictable interference particularly of secondary (non-primary carriers) in the framework of carrier aggregation, which may not be solved by conventional techniques.
Accordingly, there is a demand for mechanisms for improving carrier aggregation, particularly regarding the selection of a secondary (non-primary) carrier in the framework of carrier aggregation.